1. Field of the Invention
The invention generally relates to controlled rate release devices for volatile materials. More particularly, the invention relates to air fresheners which operate upon the principle of liquid phase transfer of a liquid fragrance composition through a microporous membrane.
2. Description of the Prior Art
Air fresheners are well known for the purpose of dispensing odorizing or deodorizing active ingredients into a particular area such as a room in a house, office, etc. Both passive and active air fresheners are available; the latter actively emitting a perfumed or deodorizing ingredient at certain intervals and the former relying on evaporation of similar, volatile ingredients. Residential air fresheners are generally passive and available in a variety of perfume-based forms and fragrances to mask unpleasant household odors and/or to provide pleasant odors. Passive air fresheners generally are produced with their active ingredients in a gel or liquid form and operate on the principle of evaporation of a perfume-based volatile liquid from a gelled mass or from a container via a wick and/or an emanator pad exposed to ambient air.
In order to be effective, passive air fresheners should ideally deliver the desired fragrance at a uniform rate over an extended period of time--i.e., a zero-order rate of release. A zero-order release rate is an essentially constant rate of release of active ingredient that is independent of either the amount of the active ingredient or its vapor pressure. However, many prior art air fresheners initially deliver a large amount of fragrance and subsequently deliver progressively less fragrance. The initial large dose is often objectionable and more than is necessary, while the later small dose is often undetectable and inadequate. To the extent all of the active ingredient is not dispensed at a constant rate, the non zero-order rate devices are costly and wasteful.
U.S. Pat. No. 4,445,641 (Baker et al.) discloses a controlled release dispenser supposedly capable of delivering essentially all of an active ingredient at a selected zero-order rate of release over a broad range of release rates. Patent '641 describes a dispenser having a microporous liquid retaining reservoir portion encased within a release rate-controlling polymeric membrane. The microporous reservoir retains liquid by capillary action. Polypropylene and other materials are suggested as suitable for the polymeric membrane and the patent also suggests the controlled release of perfumes, deodorizers and a variety of other active ingredients through such polymeric membranes.
While the Baker et al. patent does suggest utilizing polypropylene membranes with perfumes, the membranes disclosed must first be impregnated with a liquid active ingredient and the membranes disclosed are only suitable for dispensing active ingredient at a rate on the order of micrograms per day. To be effective as an air freshener the rate should be on the order of 1-20 milligrams per hour to fragrance a room of 1000 ft..sup.3 Additionally, impregnation of the membranes is an extra manufacturing step that has been found unnecessary with the present invention.
In addition to the desirability of a zero-order rate of release, it is also desirable that the fragrance released by air fresheners be uniform and undistorted over the life of the dispenser.
It is well known that the fragrant materials of air fresheners include a significant amount of volatile perfume ingredients in various proportions. Typically, the perfumes incorporated in the compositions used in air fresheners are mixtures of organic compounds admixed so that the combined odors of the individual components produce a pleasant or desired fragrance. While perfumes are generally mixtures of various materials, individual compounds may also be used as the perfume ingredient. Typical compounds for use in mixtures or individually, include methyl salicylate, d-limonene and the like.
The perfume compositions generally contain several "notes", each having different volatility rates and therefore being subject to the process of chromatography which may result in a differential distribution of the notes at various times. The various notes include a main note or the "bouquet" of the perfume composition, modifiers which round off and accompany the main note, fixatives including odorous substances that lend a particular note to the perfume throughout each of the stages of evaporation, substances which retard evaporation, and top notes which are usually low-boiling, fresh-smelling materials.
Perfumery raw materials may be divided into three main groups: (1) the essential oils and products isolated from these oils; (2) products of animal origin; and (3) synthetic chemicals. Many of these materials include such substituent groups as the carbonyl group in aldehydes and ketones; the hydroxyl groups in alcohols; the acyl group in esters; the C=O groups in lactones; nitrile groups, and the oxy moiety in ethers.
The essential oils consist of complex mixtures of volatile liquid and solid chemicals found in various parts of plants. Mention may be made of oils found in flowers, e.g., jasmine, rose, mimosa, and orange blossom; flowers and leaves, e.g., lavender and rosemary; leaves and stems, e.g., geranium, patchouli, and petitgrain; barks, e.g., cinnamon; woods, e.g., sandalwood and rosewood; roots, e.g., angelica; rhizomes, e.g., ginger; fruits, e.g., orange, lemon, and bergamot; seeds, e.g., aniseed and nutmeg; and resinous exudations, e.g., myrrh. These essential oils consist of a complex mixture of chemicals, the major portion thereof being terpenes, including hydrocarbons of the formula (C.sub.5 H.sub.8).sub.n and their oxygenated derivatives. Hydrocarbons such as these give rise to a large number of oxygenated derivatives, e.g., alcohols and their esters, aldehydes and ketones. Some of the more important of these are geraniol, citronellol and terpineol, citral and citronellal, and camphor. Other constituents include aliphatic aldehydes and also aromatic compounds including phenols such as eugenol. In some instances, specific compounds may be isolated from the essential oils, usually by distillation in a commercially pure state, for example, geraniol and citronellal from citronella oil; citral from lemon-grass oil; eugenol from clove oil; linalool from rosewood oil; and safrole from sassafras oil. The natural isolates may also be chemically modified as in the case of citronellal to hydroxy citronellal, citral to ionone, eugenol to vanillin, linalool to linalyl acetate, and safrol to heliotropin.
Animal products used in perfumes include musk, ambergris, civet and castoreum, and are generally provided as alcoholic tinctures.
The synthetic chemicals include not only the synthetically made, and naturally occurring isolates mentioned above, but also include their derivatives and compounds unknown in nature, e.g., isoamylsalicylate, amylcinnamic aldehyde, cyclamen aldehyde, heliotropin, ionone, phenylethyl alcohol, terpineol, undecalactone, and gamma nonyl lactone.
Perfume compositions as received from the perfumery house may be provided as an aqueous or organically solvated composition, and may include as a hydrotrope or emulsifier a surface active agent, typically an anionic or nonionic surfactant, in minor amount. The perfume compositions are quite usually proprietary blends of many different fragrance compounds to achieve a particular odoriferous effect.
Typically, perfume compositions contain an effective fragrancing amount of 0 to 100% by weight of the fragrance ingredient. Generally, perfume ingredient(s) are used at concentrations of about 0.1 to about 75 wt.%, based on total composition weight. The balance of the composition being one or more diluent(s), surfactant(s) and the like.
In order to produce an air freshener capable of delivering a uniform odor over an extended period of time, it is necessary to try to avoid the process of chromatography by providing a means by which all the various notes of the perfume may remain in the same proportions over time. It has been found that transmission of a perfume based composition in the liquid phase through a microporous membrane having particular characteristics produces a liquid film of the composition on one side of the membrane and the various notes of the perfume are in substantially the same proportions in the film as in the composition on the other side of the membrane. It should be noted that, as used herein, the term "liquid phase transmission" does not inolude capillarY action like that shown in the aforementioned Baker et al. patent. Chromatography occurs in such capillary action systems.
It has been noted that when liquid phase diffusion or transmission takes place (i.e., liquid passing through the membrane or film) the character of the fragrance does not vary with time. That is, the composition of the first liquid portions passing through is substantially the same as the later portions.
Membranes have long been used in delivery systems for volatile materials. One example of this is the aforementioned Baker et al. patent. Other examples are U.S. Pat. Nos. 3,951,622 (Wilk), 4,248,380 (Lee et al.), 4,614,299 (Van Lovern et al.). All of the dispensers shown in these patents utilize the principle of vapor phase migration of liquid active ingredients through a permeable membrane. However, U.S. Pat. No. 4,158,440 (Sullivan et al.) does show a dispenser utilizing the liquid phase transfer of liquid active ingredients through a specific type of permeable membrane --cellulose triacetate. Sullivan et al. did disclose that a particular microporous polypropylene film known as CELGARD.sup.R, produced by the Celanese Corporation, was also suitable in place of cellulose triacetate. However, Sullivan et al. indicates that CELGARD.sup.R acts as a liquid barrier and is permeable only to vapor which volatilizes from the liquid substance within the dispenser. This is a feature of CELGARD.sup.R that is also identified by the manufacturer. As will be understood below, the invention operates in spite of this contrary teaching.
U.S. Pat. No. 3,785,556 (Watkins) also shows a package employing liquid phase transfer through a polyethylene or polypropylene envelope via the mechanism of permeation--i.e., "diffusion by absorption not to be confused with porosity or capillarity" (1:64-67). However, it is known that membranes of conventional polypropylene (either cast or oriented) change the character and intensity of fragrances for both liquid and vapor phase transport mechanisms.
In spite of the teaching to the contrary in Sullivan et al., above, it has now been found that the invention which is the subject hereof operates with CELGARD.sup.R to produce a dispenser of volatile fragrant liquid ingredients which migrate through the CELGARD.sup.R membrane in liquid phase rather than vapor phase.
This particular membrane has a thickness of 0.5 to 5 mil with no fillers, plasticizers or extenders and has the following properties: 14000 to 20000 psi MD tensile strength, 1400 to 2000 psi TD tensile strength, 100,000 cycle folding endurance, 1 lb MD tear strength, a density of 0.28 to 0.32 oz/cubic inch, an area of 50000 to 60000 square inches per pound with 70% opacity, a moisture transmission rate of 4000 to 6000 g/square meter/day (BW method, inverted cup water method), a pore density of 10.times.10.sup.9 pores/square centimeter to 7.times.10.sup.9 pores/square centimeter and a resistance to air of 9 to 35 Gurley seconds. While the CELGARD.sup.R membrane is preferred, other membranes having these or similar properties can also be employed.
It has been found that a vent hole allowing pressure equalization inside the container is advantageous. The perfume composition used in the preferred embodiment is, for example, a neat oil or a blended perfume which will be transported across the surface of the membrane at a rate of 1 to 20 mg per hour, preferably 3-10 mg per hour, and more preferably 4-7 mg per hour, sufficient to give the desired concentration of fragrance.
The aforementioned Wilk patent discloses a permeable membrane through which a fragrance (including an essential oil and an alcohol having a molecular weight below 100, e.g. ethanol) passes substantially unchanged. However, the transmission through the membrane is only vapor phase transmission and the device is, apparently for this reason, limited to use with fragrance compositions including an essential oil and an alcohol having a molecular weight below 100. While one embodiment of Wilk appears to show a liquid fragrance within a pouch made entirely of the permeable membrane, there is no elaboration on the method of operation of this embodiment. It is assumed this embodiment also employs vapor phase transmission.
It is an object of this invention to provide a passive dispenser of volatile liquid ingredients which enables substantially all of the liquid ingredients to be dispensed over a period of time.
It is a further object of this invention to provide a passive dispenser of volatile liquid ingredients capable of dispensing same at a substantially uniform rate over the life of the dispenser.
It is another object of this invention to provide a passive dispenser capable of transmitting a composition of volatile fragrant liquid ingredients in liquid phase through a membrane in order to overcome the tendency of the various constituents of the liquid to volatilize at different rates before being exposed to the ambient environment. It is also an object of this invention to enable such liquid phase transmission while using, as the fragrance composition, a perfume having no essential oils one having, a trace amount of essential oils, or an essential oil itself.
It is another object of this invention to provide a passive dispenser capable of transmitting a volatile fragrant liquid ingredient in its liquid phase through a membrane in order to maintain the character and intensity of the fragrance before and after the transmission through the membrane.